However, the hardness differences between the first six alloys, at corresponding positions, were not very marked. This was not so for the latter two steels at distances in excess of 2 mm. from their surfaces. Alloys 11 and 13 • were appreciably softer at these positions in the carburised cases than were the other steels.
A . A • 6 In the As-Hardened Condition ' - A •A .6.1 The High Purity Steels Containing Only Vanadium as
an Alloying Addition
The hardiness values of these steels, after varying
austenitisation treatments and water quenching, are presented, in TABLE 18. Most of the hardness figures are for austeniti sation times of 20 minutes, but in some instances values are quoted for longer periods of 30 and A3 minutes.
In the case of each alloy, the maximum hardness was
attained by austenitisation at the optimum conditions to give an ideal as-hardened microstructure. These were 520, 1000 and 1120°C for Alloys 1, 2 and 3 respectively, with the soaking
time in each instance being 20 minutes. The maximum hardness values achieved for Alleys 1, 2 and 3 were 8A1 , 858 and 862
EM/30 respectively.
Differences in hardness values between these three steels were most marked after austenitisation at either very low or high temperatures. The lowest temperature employed was 850°C, but even after austenitisation at this temperature for 20
However,.Alloy 2 had a lower hardness of 812 HV/30 and Alloy 3 a very low value of 772 HV/30 as a result of austenitisation under these.conditions. The hardness of the latter steel was increased to 803 HV/30 after austenitising at 900°C for 20 minutes.
Austenitisation of Alloy 1 at temperatures in excess of 1 050°C caused a considerable decrease in hardness. This was particularly so after austenitising at 1150 and 1200°C for 20 minutes, as a result of which the hardness figures were 762 and 702 KV/30 respectively.
This effect was not nearly so marked in the cases of Alloys 2 and 3* The former steel did show a slight decrease
in hardness after austenitisation at temperatures above 1100°C, but still had a value of 786 HV/30 after austenitising at
1200°C for 20 minutes. However, in the case of Alloy 3 there was only a fractional fall in hardness after austenitisation at temperatures in excess of 1120°C. This steel in fact had a hardness of 836 HV/30 after austenitisation at 1200°C for 20 minutes and subsequent water quenching.
Increasing the austenitisation time to 30 and k5 minutes at certain temperatures had very little effect on the hardness values obtained for these steels after 20 minutes soak at the corresponding temperature, followed by water quenching.
There was, however, one exception, this being Alloy 1 after austenitisation at 1150°C. The hardness of this steel after austenitising at this temperature and subsequent quenching was 762 HV/30, whilst this was reduced to 7AA and 721 HV/30 as a result of increasing the soaking period to 30 and A5
minutes respectively, at this same temperature.
U.U.6.2 The High Purity Steels Containing Vanadium and a
Second Alloying Addition
Peak hardnesses for these steels were attained hy
O-
austenitisation in the temperature range 1100 to 1150 , for a time of 20 minutes, followed by water quenching. The hard ness values of all these alloys, after austenitisation
treatments at varying temperatures, are presented in TABLE 19 Austenitisation at 850°C resulted in all the steels havi low hardness values, most of which were below 810 HV/30.
However, raising the austenitising temperature to 900°C cause increases in the hardness figures of most of the alloys. Th exception to this was Alloy 5 (Ho), which had a. value of
796 HV/30.
Generally, austenitisation at temperatures between 950 and 1050°C resulted in increases in hardness readings of the alloys. All the steels had hardnesses in excess of 800 HV/3 after austenitising at 950°C for 20 minutes and subsequent water quenching, and in some cases these were of the order
850 to 860 HV/30 after treatment at 1050°C.
Peak hardness values were obtained by austenitising eith under, or very close to, the conditions required to give the ideal microstructure of each particular alloy, as was the cas for Alloys 1 , 2 and 3* Maximum hardnesses for Alloys 6 (An), 7(Ni) and 9(Co).were attained by austenitisation in the range 1100 to 1120°C, whilst this was the case for Alloys L/Si), 5 (Mo), 8(Or) and 10(V ) between 1120 and 1150°C. Austenitisc tion of these steels at 12C0°C resulted in decreases in hardn of ap.proximately 30 KV/30, compared with the corresponding value obtained after treatment at 1150°C, with the exception
of Alloy 7(Ni) which softened more appreciably.
In every case, with the exception of austenitisation at 950°C, Alloy 9 (Co) had the lowest hardness of these steels
after corresponding treatments. The maximum hardness of this
steel was attained after austenitising at 1120°C, the value
only being 830 fiV/30.
The peak hardness values of the other steels were in a range 856 to 888 HV/30. In the lower part of this range were Alloys i|(Si), 6(Mn) and 7(Ni) whilst Alloys 3 (Mo), 8(Cr) and
r
10(W) had maximum hardness readings of 877* 879 and 888 HV/30 respectively.
k .k. 6.3 The Commercial Furlt.v Steels
The carburised steels had all been given optimum austeni tisation treatments. These conditions were austenitising at 860°C in the cases of Alloys 11 and 15* 900°C for Alloys 12 and 16, 9hO°C for Alloys 13 and 17* and 10h-0°C in the cases of Alloys 1h and 18. In each instance the soaking period was 20 minutes, and the quenchant employed was water.
The form of the graph of hardness against the distance from the surface of the specimen was the same for each of the carburised steels, as shown in FIGS. 98 and 97« From the sample surface to a distance 2.5 mm. within, there was only a relatively slight decrease in hardness. This is illustrated in the instance of Alloy 11, where the hardness reduction was
U5 HV/5.
Between 2.5 and 2.75' mm. from the surface of each specimen,